I have some video files I need to get up on YouTube and other such things, but the files are a little oversized. Could someone direct me in how to compress them in such a way that I could upload them to such websites please?

If you're using Windows XP the easiest way would be to use Windows Movie Maker, which comes bundled with the system. It can only convert files to Windows Media format, but as you're going to put it up on YouTube you probably don't care about the video quality anyway :P